1. Field of the Invention
The present invention relates to a structure for coupling a differential assembly installed in an automobile with the right and left drive shafts connected to the right and left traction wheels. More particularly, the invention relates to a limited slip differential assembly.
2. Description of the Related Art
The power transmission mechanism of vehicles includes a differential assembly through which power is transmitted and the right and left drive shafts which transfer the drive force supplied to the differential assembly to the right and left traction wheels, respectively.
The differential assembly includes a differential carrier mounted on the vehicle body and a differential case installed inside the differential carrier. The differential case has the right and left end portions that are rotatably supported by the differential carrier, for example, via bearings. Accordingly, the differential case is prohibited from moving in the right and left direction, i.e., in the axial direction of the drive shafts with respect to the differential carrier.
The differential assembly includes: right and left side gears which the right and left drive shafts each mate with splines; a pinion shaft disposed between the right and left side gears; pinion gears which are rotatably supported at both end portions of the pinion shaft and mate with the right and left side gears, respectively; and a tubular differential case that accommodates these members. The assembly is configured such that the end portions of the pinion shaft fit in the through holes formed in the outer circumferential wall of the differential case, respectively, thereby prohibiting the pinion shaft with a washer or the like from radially moving.
In contrast to such a typical, differential assembly, there is another type of differential assembly known as a limited slip differential assembly which includes right and left friction clutches, right and left pressure rings, and a cam mechanism. The friction clutches are configured such that a plurality of friction clutch disks are disposed, to be movable in the direction of the axle shaft, between the shaft portion of right and left side gears and the differential case. The pressure rings are disposed opposite to each other to cover each of the right and left side gears, and moved away from each other in the direction of the axle shaft, thereby pushing each of the right and left friction clutches outwardly in the direction of the axle shaft. The cam mechanism expands the spacing between the pair of right and left pressure rings in the direction of the axle shaft. The cam mechanism is composed of a cam surface portion 60 which is formed circumferentially, for example, at four points on the opposing portions of the pair of right and left pressure rings, and a cam portion which is formed at each shaft end portion of a pinion shaft formed in the shape of a cross and engages with the cam surface.
Here, the right and left drive shafts are coupled to prevent movement in both directions along the axle shaft with respect to the differential assembly and the limited slip differential assembly, maintaining the distance between the right and left traction wheels. The right and left drive shafts may be coupled to the differential assembly, for example, in a type of structure, as disclosed in Patent Document 1, with the drive shafts having a constant outer diameter. Now, a description will be made to this coupling structure with reference to FIG. 3.
FIG. 3 shows a half of a differential assembly 1 whose right half with respect to a center line CL is a typical differential assembly. In FIG. 3, right and left drive shafts 4 and 5 each have a circumferential groove 6 at their one inner axial end portion and are attached with tires (traction wheels) 2 and 3 at the other end, respectively. Here, let the distance between the right and left tires be L. As illustrated, there is a side gear 7 on the right side with respect to the center line CL. The gear 7 has, on an inner end face opposing the center line CL, a recessed portion 9 formed around a shaft hole 8 through which the drive shaft 5 passes. The circumferential groove 6 receives a disk-shaped stopper disk 10 which fits into the recessed portion 9, prohibiting the drive shaft 5 from becoming dislodged. The inner end of the drive shaft 5 is brought into contact with a pinion shaft 11 to prevent the drive shaft 5 from being pushed in, thereby maintaining the distance L between the right and left tires.
The pinion shaft 11 is attached rotatably at an end portion thereof with a pinion gear 12, and engages, at its end portions, with the cylindrical portion of a differential case 13. In addition, the differential case 13 is provided securely on its outside with a ring gear 14. Then, the ring gear 14 and the differential case 13 are accommodated in a differential carrier 15.
In such a drive shaft coupling structure for a differential assembly, the stopper disk 10 is either mounted or extracted under such a condition that the pinion shaft 11 has been drawn out of the differential case 13 and the drive shaft 5 has been pushed towards the center line CL. The differential case 13 is provided with a large maintenance opening for exposing the components under the condition as illustrated, thereby allowing the pinion shaft 11 formed of a single shaft to be extracted. This would make it possible to move the drive shaft 5 by a small distance towards the center line CL, thus facilitating the extracting and mounting of the stopper disk 10 through the maintenance work opening.
[Patent Document]
[Patent Document 1] U.S. Pat. No. 7,270,026
In a vehicle equipped with the typical differential assembly shown in FIG. 3, suppose that the differential assembly is replaced with a limited slip differential assembly. In this case, the following method is advantageous in terms of costs and easiness in the replacement. That is, only the differential case and those various types of additional components to be disposed for the limit slip differential assembly within the differential case may be incorporated, without replacing the differential carrier 15, the ring gear 14, and the drive shafts 4 and 5.
In this case, as shown on the left side of the center line CL in FIG. 3, modifications may be made to the shape and size of a differential case 20 and a side gear 21. Furthermore, the assembly is additionally provided with a friction clutch 22, a pressure ring 23 shown in a chain double-dashed line, a pinion shaft having a generally cross-like shape, and a cam mechanism.
However, to use the differential carrier 15 again, the distance between the right and left of the new differential case 20 is restricted to the inter-bearing distance L1 between the right and left bearing portions 16 which support the respective right and left end portions of the differential case 13 inside the differential carrier 15.
On the other hand, the new side gear 21 has a gear portion 24 formed on the center line side, and a shaft portion 25 formed axially outwardly to carry the friction clutch 22, resulting in the entire length being axially greater than the side gear 7 of a typical differential assembly 1. Furthermore, due to the restriction that the dimensions of each member in the direction of the axle shaft have to be determined within the aforementioned distance L1, the gear portion 24 of the new side gear 21 inevitably extends beyond the inner end of the drive shaft 4 towards the pinion shaft 11.
The inner end of the drive shaft 4 to be inserted into a shaft hole 26 of the new side gear 21 is located deeper than the inner end of the shaft hole 26. Thus, the stopper disk 10 cannot be received in the circumferential groove 6 of the drive shaft 4 to prevent it from becoming dislodged.
Furthermore, the limited slip differential assembly is configured such that four pinion shafts are assembled in the shape of a cross and each pinion shaft is attached at the end portion thereof with a pinion gear. In addition, the side gear is covered with the pressure ring 23. It is thus not possible to couple the drive shafts using the stopper disk 10.